The invention relates to a bending arrangement for aluminum profile.
Spherical tanks used for storage and transport of liquefied gas are large, normally about 40 m in diameter and are made of aluminum alloy. As used herein, the term "aluminum" includes an aluminum alloy suitable for use in fabrication of a spherical tank for storage and transport of liquefied gas, particularly liquefied natural gas. At the equator area of a large spherical tank, a special profile is used, which has to be formed to the desired curvature by press bending straight workpieces. The equator profile workpieces that are bent are normally about 15 m in length and about 1 m in height and have a thickness of close to 200 mm and a mass of more than 5000 kg. The completed workpiece must meet high demands with respect to dimensional accuracy. Because of the size of the workpiece, bending, check measuring and final control of the bending is difficult to perform. In particular the reflection or springback of the workpiece must be taken into account in the measuring and bending process. Also accurate moving of the workpiece in the press is difficult due to its great weight. Furthermore, the equator profile is asymmetric in cross-section relative to a central horizontal plane, typically being thicker at points below the central plane than at corresponding points above the central plane. Consequently, there is a tendency for the profile to twist during the bending process and so it is generally necessary either to take special steps to prevent twisting during the bending process or to carry out correction steps to remove the twisting after the bending process.
Prior art bending arrangements are disclosed in e.g., U.S. Pat. No. 3,333,445 and Japanese Publications JP 61199517 and JP 61199518. These arrangements relate to bending of generally symmetric workpieces taking into account reflection or springback already during the bending stage. Prior art measures for controlled movement of the workpiece are disclosed in Japanese Publication JP 5131330.